This invention relates to processes for foaming polymer compositions, compositions useful for preparing foamed polymer compositions and solid foamed polymer compositions.
Foamed polymer compositions are cellular structures which typically comprise a gas dispersed throughout a solid. Such foamed compositions can exhibit a lower density and weight, but a substantially equivalent strength to non-foamed compositions. An example of a commercial foamed thermoplastic polymer composition is a polycarbonate polymer foamed with 5-phenyl tetrazole compound.
Polycarbonate polymers are derived from reactions of dihydroxy organic compounds. Commonly used polycarbonates are derived from dihydric phenols and carbonic acids or derivatives such as phosgene. Such thermoplastic polymers are suitable for the manufacture of molded parts wherein impact strength, rigidity, toughness, heat resistance and excellent electrical properties are desired.
Thermoplastic polymer compositions are foamed by dispersing a blowing or foaming agent throughout the polymer composition at a temperature at which the polymer composition is thermoplastic and the foaming agent is stable. The polymer composition and foaming agent are then subjected to conditions under which the foaming agent decomposes into gaseous products which can cause the volume of the polymer composition to increase. Unfortunately, many foaming agents, including 5-phenyl tetrazole, decompose into products which adversely affect the polymer composition. For example, the decomposition products of 5-phenyl tetrazole undesirably react with polycarbonate polymers, lowering the molecular weight, and causing brittleness in the final polycarbonate foam.
In view of the disadvantages of known methods, it would be desirable to foam polymer compositions using foaming agents whose degradation products do not adversely affect the polymer compositions in which they are used.